The present invention relates to a drive control technology for brushless motors and a technology effectively applicable to start-up control on three-phase direct-current motors. More particularly, it relates to a technology that can be effectively utilized for a drive control device of a spindle motor that rotatably drives storage media in a desk-type storage device, such as a hard disk unit (hard disk driver).
To rotate a magnetic disk as storage media in a hard disk unit, a brushless three-phase direct-current motor designated as spindle motor is in general use. A magnetic disk is rotated at high speed by a spindle motor, and a magnetic head for read/write is brought close to the surface of the rotating magnetic disk and moved in the radial direction to write or read information.
The following method has be conventionally used in drive control on a brushless motor: the positional relation between rotor and stator is detected using a Hall element; a coil phase with which energization should be started is determined from the detected positional relation to prevent the reverse rotation of the motor. However, sensorless motors have been brought into greater use with respect to hard disk units. This is because, when a motor is provided with a rotor position detector using a Hall element, it is difficult to reduce the size of the equipment. Such sensorless motors have a problem. If the positional relation between rotor and stator is unknown when the rotation of a motor is started, the rotor can make a reverse rotation.
To cope with this, the present applicants proposed the following control method: so short a pulse current that a rotor does not react is passed through any coils in two phase; the polarity of an induced voltage that occurs in the non-conducting phase is detected to determine the positional relation between rotor and stator; the characteristic that the polarity of an induced voltage is switched every 180° of electrical angle is utilized to determine a phase with which energization should be started; the reverse rotation of this sensorless motor at start-up is thereby avoided. (Refer to Patent Document 1.)    [Patent Document 1] Japanese Unexamined Patent Publication No. 2001-275387    [Patent Document 2] Japanese Unexamined Patent Publication No. 2004-140975